1. Field of the Invention
The present invention relates to relay multiplexers for multiplexing input or output signals, such as in instrumentation/data acquisition (DAQ) systems, and more particularly to an improved relay multiplexer system which provides improved safety from shock hazards.
2. Description of the Related Art
Scientists and engineers often use instrumentation or DAQ systems to perform a variety of functions, including test and measurement, laboratory research, process monitoring and control, data logging, analytical chemistry, test and analysis of physical phenomena, and control of mechanical or electrical machinery, to name a few examples.
A typical computer-based instrumentation system comprises a computer system with instrumentation hardware, one or more transducers, and signal conditioning logic coupled between the transducers and the instrumentation hardware. The transducers or other detecting means convert the physical phenomena being measured into electrical signals, such as voltage or current, measurable by the instrumentation hardware. Examples of transducers include thermocouples (temperature to voltage), RTDs (temperature to electrical resistance), strain gauges (strain to voltage), and microphones (sound to voltage).
In a computer-based system, the instrumentation hardware or device is typically an expansion card plugged into one of the I/O slots of the computer system. In another common instrumentation system configuration, the instrumentation hardware is coupled to the computer system via other means such as through a VXI (VME eXtensions for Instrumentation) bus, a GPIB (General Purpose Interface Bus), a serial port or bus, or parallel port of the computer system. The instrumentation hardware may be a data acquisition (DAQ) card, a multimeter card, or other type of instrumentation device.
The instrumentation device enables the computerized measurement and generation of real world analog and digital signals. The instrumentation device, e.g., a DAQ device, a multimeter device, etc., typically includes one or more analog to digital (A/D) converters (ADCs), digital to analog (D/A) converters (DACs), digital I/O ports, and counter/timer circuits.
The instrumentation hardware is configured and controlled by software executing on the computer system. The software for configuring and controlling the instrumentation system typically comprises driver software and the instrumentation application software, or the application. The driver software serves to interface the instrumentation hardware to the application and is typically supplied by the manufacturer of the instrumentation hardware or by a third party software vendor. The application is typically developed by the user of the instrumentation system and is tailored to the particular function which the user intends the instrumentation system to perform. The instrumentation hardware manufacturer or third party software vendor sometimes supplies application software for applications which are common, generic or straightforward.
The signal conditioning logic may include relay multiplexers which multiplex a plurality of signals into the instrumentation device. A relay multiplexing module is used when the device(s) under test (DUT) present a plurality of signals to the instrumentation device. The relay multiplexing module comprises a set of switches that bring one signal at a time to the input of the instrumentation device to be measured. The relay multiplexer module time multiplexes a plurality of channels to 1 channel by sequentially closing one or more relays at a time.
When a large number of input signals are desired to be provided to the instrumentation device, then typically two or more relay multiplexer modules are used to multiplex the input signals. In this instance, an analog bus is used to interconnect the signals from the multiplexer modules. The analog bus allows the user to daisy chain the multiplexer modules or place them in parallel to provide a signal count much higher than 1 relay multiplexer or switch can provide. For example, the SCXI standard includes an analog bus for this purpose.
Instrumentation systems are often used to measure high voltage signals. In this instance the high voltage signals are provided through the relay multiplexers. When one or more conventional relay multiplexers are used in the measurement of high voltage signals, this may inadvertently expose an operator to these hazardous voltages.
For example, some relay multiplexers, such as for VXI, include two or more connectors which potentially can route high voltage signals from one connector back onto the connector pins of an un-used connector, where they are exposed to the user. Also, problems can arise when two or more relay multiplexers are used to multiplex the input signals to an analog bus. In this instance one relay may be closed, presenting a high voltage on the analog bus. This may, for example, cause a high voltage to be received by another relay module and provided back out another channel to the user. If a connector is plugged into the second relay multiplexer module, there is no safety hazard to the user because the pins are enclosed by the connector. However, if the connector is removed or off during this instance, thereby exposing the connector pins, then one of the signal pins may present a very high voltage, hence presenting a safety hazard.
Therefore, an improved relay multiplexer system is desired which provides improved safety during the measurement of high voltage signals.
The present invention comprises a relay multiplexing system which provides improved safety from hazardous voltage conditions. The relay multiplexing system comprises a relay multiplexer module and a terminal block which connects to the relay multiplexer module. The relay multiplexer module and corresponding terminal block incorporate a design according to the present invention whereby power can only be provided to the respective relays when the corresponding terminal block is connected to the respective relay multiplexer module. When the terminal block is removed from the corresponding relay multiplexer module, power is unable to be provided to the relays, thereby ensuring safety from hazardous voltages.
The relay multiplexer module includes a power supply, a plurality of relays, and a front connector. The plurality of relays each include a power input which is adapted to be coupled to the power supply to control operation of the relays. The front connector includes a first pin connected to the power supply and a second pin which is connected to the power input of each of the plurality of relays. The terminal block is adapted to connect to the front connector of the relay multiplexer module, wherein the terminal block electrically connects the first and second pins of the front connector when the terminal block is connected to the relay multiplexer module. Thus, when the terminal block is connected to the relay multiplexer module, an electrical path is created from the power supply, through the terminal bock, and then back to the relays, thereby selectively enabling operation of the relays. When the terminal block is removed from the relay multiplexer module, the electrical path is disconnected, thereby disabling operation of the relays.